The present invention relates generally to a hybrid electric vehicle (HEV), and specifically to a strategy to control a split powertrain HEV to achieve maximum wide open throttle (WOT) acceleration performance.
The need to reduce fossil fuel consumption and emissions in automobiles and other vehicles predominately powered by internal combustion engines (ICEs) is well known. Vehicles powered by electric motors attempt to address these needs. Another alternative solution is to combine a smaller ICE with electric motors into one vehicle. Such vehicles combine the advantages of an ICE vehicle and an electric vehicle and are typically called hybrid electric vehicles (HEVs). See generally, U.S. Pat. No. 5,343,970 to Severinsky.
The HEV is described in a variety of configurations. Many HEV patents disclose systems where a driver is required to select between electric and internal combustion operation. In other configurations, the electric motor drives one set of wheels and the ICE drives a different set.
Other, more useful, configurations have developed. For example, a series hybrid electric vehicle (SHEV) configuration is a vehicle with an engine (most typically an ICE) connected to an electric motor called a generator. The generator, in turn, provides electricity to a battery and another electric motor, called a traction motor. In the SHEV, the traction motor is the sole source of wheel torque. There is no mechanical connection between the engine and the drive wheels. A parallel hybrid electrical vehicle (PHEV) configuration has an engine (most typically an ICE) and an electric motor that work together in varying degrees to provide the necessary wheel torque to drive the vehicle. Additionally, in the PHEV configuration, the motor can be used as a generator to charge the battery from the power produced by the ICE.
A parallel/series hybrid electric vehicle (PSHEV) has characteristics of both PHEV and SHEV configurations and is sometimes referred to as a powersplit configuration. In one of several types of PSHEV configurations, the ICE is mechanically coupled to two electric motors in a planetary gear-set transaxle. A first electric motor, the generator, is connected to a sun gear. The ICE is connected to a carrier gear. A second electric motor, a traction motor, is connected to a ring (output) gear via additional gearing in a transaxle. Engine torque can power the generator to charge the battery. The generator can also contribute to the necessary wheel (output shaft) torque if the system has a one-way clutch. The traction motor is used to contribute wheel torque and to recover braking energy to charge the battery. In this configuration, the generator can selectively provide a reaction torque that may be used to control engine speed. In fact, the engine, generator motor and traction motor can provide a continuous variable transmission (CVT) effect. Further, the HEV presents an opportunity to better control engine idle speed over conventional vehicles by using the generator to control engine speed.
The desirability of combining an ICE with electric motors is clear. There is great potential for reducing vehicle fuel consumption and emissions with no appreciable loss of vehicle performance or drivability. The HEV allows the use of smaller engines, regenerative braking, electric boost, and even operating the vehicle with the engine shutdown. Nevertheless, new ways must be developed to optimize the HEV""s potential benefits.
One such area of HEV development is controlling a powersplit HEV to achieve wide open throttle (WOT) acceleration performance at various speeds especially when an engine is not running. Any successful HEV implementation should consider that drivability and performance of the vehicle should at least be comparable to a conventional ICE powered vehicle.
HEV controllers are known in the prior art. Severinsky describes a simplistic HEV control unit to determine acceleration based on accelerator position and a processor to use the motor up to about 25 mph then in combination with the ICE for high-speed acceleration. U.S. Pat. No. 5,755,303 to Yamamoto et al. describes continuously variable transmissions that allow each powertrain source to operate efficiently. U.S. Pat. No. 5,775,449 to Moroto et al. during hi-torque requirements suspends generator functions and increases engine torque by reducing clutch slippage. U.S. Pat. No. 5,915,488 to Fliege describes a safety mechanism to reduce power to an electric motor if damaging amounts of acceleration are detected. U.S. Pat. No. 6,054,844 to Frank discloses an overall HEV control system for an ICE using a continuously variable transmission engine to operate at xe2x80x9cwide open throttlexe2x80x9d (WOT), or along the xe2x80x9cIdeal Torque/Speed Operating Linexe2x80x9d (IOL) for best efficiency and lowest emissions. U.S. Pat. No. 6,11 6,363 to Frank describes a system that when operating in the HEV mode, the ICE operates at high throttle settings and, when the ICE is operating at wide open throttle (WOT) but additional power is still required, the driver depresses the pedal further and electric motor torque is automatically added. Therefore, vehicle acceleration is proportional to the accelerator pedal position as in a conventional car.
Unfortunately, no precise strategy is known to control a split powertrain HEV that attempts to coordinate the HEV""s power sources (traction motor, generator motor, engine) to satisfy driver demand and expectation for wide open throttle (WOT) acceleration performance while optimizing the total powertrain system efficiency and performance such as when an engine is not even operating. Further precision to include battery conditions such as output capacity, temperature, and state of charge are also needed.
Accordingly, the present invention provides a strategy to control a split powertrain hybrid electric vehicle (HEV) to coordinate the HEV""s power sources to satisfy driver demand and expectation for wide open throttle (WOT) acceleration performance at any speed while optimizing the total powertrain system efficiency and performance, especially when the engine is not even running.
Specifically, the invention provides a control system for an HEV powertrain powered by at least one of an engine, a traction motor, and a generator motor comprising sensors for accelerator position, vehicle speed, and gear selector (PRNDL) position. The HEV has a battery for powering the traction motor and generator motor and receiving power from the generator motor. The control of the present invention can receive input from the accelerator position sensor, vehicle speed sensor, and PRNDL position sensor; make a determination of whether full forward acceleration is requested (D or L); making a determination of whether the engine is running; estimate the sum torque of the traction motor and the generator motor if the engine is not running, calculating the maximum sum torque output of the traction motor and the engine, comparing the estimated sum torque of the traction motor and the generator motor with the calculated sum torque output of the traction motor and the engine, and starting the engine if the estimated sum torque of the traction motor and the generator motor is less than the calculated sum torque output of the traction motor and the engine for a given vehicle speed.
In one embodiment of the present invention, battery sensors connected to the battery and VSC can be added for battery operating capacity, temperature and state of charge. These sensors can add even more precision to the estimating of the sum torque of the traction motor and the generator motor and the calculating of the maximum sum torque output of the traction motor and the engine.
In another embodiment of the present invention, the control system can use a constant to allow a prestart of the engine when estimating the sum torque of the traction motor and the generator motor and the calculating of the maximum sum torque output of the traction motor and the engine.
Other objects of the present invention will become more apparent to persons having ordinary skill in the art to which the present invention pertains from the following description taken in conjunction with the accompanying FIGS.